Small Form-factor Pluggable (SFP) units represent one example of standardized hot-pluggable transceiving units. SFP units are standardized units adapted to be inserted within a chassis. A suite of specifications, produced by the SFF (Small Form Factor) Committee, describe the size of the SFP unit, so as to ensure that all SFP compliant units may be inserted smoothly within one same chassis, i.e. inside cages, ganged cages, superposed cages and belly-to-belly cages. Specifications for SFP units are available at the SFF Committee website.
SFP units may be used with various types of exterior connectors, such as coaxial connectors, optical connectors, RJ45 connectors and various other types of electrical connectors. In general, an SFP unit allows connection between an external apparatus (via a front connector of the SFP unit having one of the aforementioned types) and internal components of a hosting unit (via a back interface of the SFP unit). Examples of the internal components of the hosting unit include a motherboard, a card or a backplane leading to further components, etc. Specification no INF-8074i Rev 1.0, entitled “SFP (Small Form-factor Pluggable) Transceiver, dated May 12, 2001, generally describes sizes, mechanical interfaces, electrical interfaces and identification of SFP units.
The SFF Committee also produced specification no SFF-8431 Rev. 4.1, “Enhanced Small Form-factor Pluggable Module SFP+”, dated Jul. 6, 2010. This document, which reflects an evolution of the INF-8074i specification, defines, inter alia, high speed electrical interface specifications for 10 Gigabit per second SFP+ modules and hosts, and testing procedures. The term “SFP+” designates an evolution of SFP specifications.
INF-8074i and SFF-8431 do not generally address internal features and functions of SFP devices. In terms of internal features, they simply define identification information to describe SFP devices' capabilities, supported interfaces, manufacturer, and the like. As a result, conventional SFP devices merely provide connection means between external apparatuses and components of a hosting unit, the hosting unit in turn exchanging signals with external apparatuses via SFP devices.
Recently, SFP units with internal features and functions providing signal processing capabilities have appeared. For instance, some SFP units now include signal re-clocking, signal reshaping or reconditioning, signals combination or separation, signal monitoring, etc.
In the field of video transport, advances have been made recently for transporting the payload of a video signal into Internet Protocol (IP) packets (e.g. Serial Digital Interface (SDI) video payloads encapsulated into IP packets). Furthermore, SFP units have been adapted to provide the following functionalities: a first SFP unit transforms an SDI signal transporting a video payload into an IP flow, the IP flow is transported over an IP networking infrastructure, and a second SFP unit transforms the IP flow back into an SDI signal transporting the video payload.
There are several issues with the transport of video payloads on an IP networking infrastructure. One issue is that an IP packet transporting a video payload may be delayed, or even lost. Since video is a time sensitive application, and in some cases a high level of image quality may be a requirement, issues related to packet delay and packet loss need to be addressed.
One way to address the issue of packet delay and packet loss is to generate two duplicate IP flows for transporting the same video payload. The two duplicate IP flows use two separate IP paths in the IP networking infrastructure. A receiver receives the two separate IP flows and uses the packets of the “best” IP flow to extract the video payload. The “best” IP flow is determined based on one or more metrics determined for each of the duplicate IP flows, such as packet delay, packet loss rate, etc. However, using two duplicate IP flows doubles the bandwidth used for transporting the video payload on the IP networking infrastructure.
At the receiver level, flow switching is generally implemented for switching from a first IP flow corresponding to a first video source to a second IP flow corresponding to a second video source. A Join Before Leave” approach is generally used, where the first and second IP flows are received simultaneously for a short period of time, in order to perform a smooth transition between the first and second video sources. Before the transition, only the first video IP flow is received; and after the transition, only the second video IP flow is received.
Combining the “Join Before Leave” approach and the use of duplicate IP flows, during the short period of time for performing the smooth transition, four IP flows are simultaneously transported over the IP networking infrastructure. A single video payload is extracted by the receiver based on the four IP flows. The extracted video payload is for example outputted by the receiver in the form of an SDI signal transporting the extracted video payload. The four simultaneous IP flows consist of two duplicate IP flows corresponding to the first video source, and two duplicate IP flows corresponding to the second video source. The burden on the IP network infrastructure is heavy, since each IP flow transporting a video payload requires an important amount of bandwidth, typically in the order of several Gigabits per second.
Another approach to flow switching having a lower impact on the IP networking infrastructure consists in a “Leave Before Join” approach. In this approach, the last frame of the first video source is frozen, so that the receiver can leave the first IP flow first, and then join the second IP flow. Although this approach may be acceptable in certain use cases, it does not provide a seamless flow switching,
Therefore, there is a need for a new method implemented by a standardized hot-pluggable transceiving unit for performing optimized flow switching.